Chapter 5: Overhead or Under-Floor Installation?

Cisco Press

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When routing infrastructure overhead, structured cabling and electrical conduits are typically installed above the Data Center suspended ceiling, routed by cable trays or ladder racks and terminated in raceways below the ceiling. Provide space between automatic sprinkler heads mounted in the false ceiling and any solid objects such as raceways, cable trays, server cabinets, or other Data Center equipment; building codes in many regions call for a minimum clearance of 18 inches (45.7 centimeters). To keep power and data adequately separated, route them in back-to-back raceways, with power over the front of server cabinet locations and data over the back.

When routing infrastructure under floor, begin by establishing the height of the raised floor system. The higher the elevation, the greater the volume of cooled air that can pass through the plenum, and the less obstruction that is presented by infrastructure installed along the subfloor. Floor heights of 18 or 24 inches (45.7 or 61 centimeters) are typical.

Unless you create a Data Center with a sunken subfloor, which requires a compatible building design and additional expense, you must bring equipment onto the raised floor by way of a ramp or lift. Ramps are the most common, and are sized based upon the height of the floor. The taller the floor, the longer the ramp must be. Lifts are a second, more expensive alternative in which equipment is placed on a platform and then elevated to match the height of the Data Center floor.

A critical element of a Data Center raised floor is its weight-bearing ability. The more it can support, the more servers and networking equipment that can potentially be installed in the room. Strive for a raised floor that can support 1500, 2000, or more pounds per floor tile—or whatever the maximum strength of the building is, whichever is greater. Servers are becoming heavier each year, and you want your Data Center to be able to support future equipment.

Three types of floor panels are used in the raised floor system: solid tiles, which are the strongest; perforated tiles, which control airflow; and notched tiles that enable cabling to connect from server cabinets to under-floor infrastructure. Caps or other air-blocking devices may be placed in panel cutouts to prevent air from being misdirected.

Under-floor infrastructure can be terminated in several ways. The most flexible design is to run individual electrical conduits and cable bundles to each server cabinet location. Cable trays and raceways may also be used. If you do install raceways, seek components that are easily reconfigured or expandable. A final option is to terminate directly into Data Center cabinets. This is the least flexible design, but removes the slight risk of patch cords or power cables being damaged when someone lifts or replaces floor tiles.

Properly seal the subfloor to avoid concrete dust in the room.

Common infrastructure-related problems include improper placement or sizing of tile cutouts, installation of non-plenum cabling in plenum spaces, or failing to design a strong-enough raised floor.

Copyright © 2007 Pearson Education. All rights reserved.

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Copyright © 2007 IDG Communications, Inc.

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